Margin: How Does It Work?

In the same way a bank can lend you money if you have equity in your house, your brokerage firm can lend you money against the value of the investments in your portfolio.

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n much the same way that a bank can lend you money if you have equity in your house, your brokerage firm can lend you money against the value of certain stocks, bonds, and mutual funds in your portfolio. Such funds are called a margin loan, and you can use them to buy additional securities or even for short-term needs not related to investing.
Each brokerage firm can define, within certain guidelines, which stocks, bonds, and mutual funds are marginable. The list usually includes securities traded on the major U.S. stock exchanges that sell for at least $5 per share, though certain high-risk securities may be excluded. Investments in retirement accounts or custodial accounts aren't eligible.

How does margin work?

Brokerage customers who sign a margin agreement can generally borrow up to 50% of the purchase price of new marginable investments (the exact amount varies depending on the investment). As we'll see below, that means an investor who uses margin could theoretically buy double the amount of stocks than if they'd used cash only. Most investors borrow less than that because—the more you borrow, the more risk you take on—not to mention the interest costs you'll have to pay—but 50% makes for simple examples.
For example, if you had $5,000 cash in a margin-approved brokerage account, you could buy up to $10,000 worth of marginable stock: You would use your cash to buy the first $5,000 worth, and your brokerage firm would lend you another $5,000 for the rest, with the marginable stock you purchased serving as collateral.
The total amount you can deploy using margin is known as your buying power, which in this case amounts to $10,000. (Schwab clients may check their buying power by clicking on the "Buying Power" link at the top of the Trade page on Schwab.com).


Source: Schwab.com.

New securities aren't the only source of collateral. You can also often borrow against the marginable stocks, bonds, and mutual funds already in your account. For example, if you have $5,000 worth of marginable stocks in your account and you haven't yet borrowed against them, you can purchase another $5,000. The stock you already own provides the collateral for the first $2,500, and the newly purchased marginable stock provides the collateral for the second $2,500. You now have $10,000 worth of stock in your account at a 50% loan value, with no additional cash outlay.
Because margin uses the value of your marginable securities as collateral, the amount you can borrow fluctuates day to day as the value of the marginable securities in your portfolio rises and falls. If the value of your portfolio rises, your buying power increases. If it falls, your buying power decreases.

Margin interest

As with any loan, when you buy securities on margin you have to pay back the money you borrow plus interest, which varies by brokerage firm and the amount of the loan.
Margin interest rates are typically lower than those on credit cards and unsecured personal loans. There's no set repayment schedule with a margin loan—monthly interest charges accrue to your account, and you can repay the principal at your convenience. Also, margin interest may be tax deductible if you use the margin to purchase taxable investments and you itemize your deductions (subject to certain limitations; consult a tax professional about your individual situation).